This invention relates to flexible intumescent sheets useful as firestops or as mounting mats for catalytic converters and diesel particulate filters or traps and particularly to flexible multilayer intumescent sheets that have at least two layers that form a single sheet without auxiliary bonding materials.
Pollution control devices are employed on motor vehicles to control atmospheric pollution. Such devices include catalytic converters and diesel particulate filters. Catalytic converters typically contain a ceramic monolithic structure which supports the catalyst. The monolithic structure may also be made of metal. Diesel particulate filters or traps are wall flow filters which have honeycombed monolithic structures typically made from porous crystalline ceramic materials.
Each of these devices has a metal housing (typically stainless steel) which holds a ceramic or steel monolithic structure. The ceramic monolithic structures generally have very thin walls to provide a large surface area for the catalyst and are fragile and susceptible to vibration damage and breakage. The ceramic monolithic structures or monoliths have a coefficient of thermal expansion generally an order of magnitude less than the metal housing which contains them. To avoid damage to the ceramic monoliths from road shock and vibrations, to compensate for the thermal expansion difference, and to prevent exhaust gases from passing between the monoliths and the metal housings, ceramic mats or paste materials are disposed between the ceramic monoliths and the metal housings. The process of placing or disposing of the mounting material or mat is also called canning and includes such processes as injecting a paste into a gap between the monolith and the metal housing, or wrapping a sheet or mat material around the monolith and inserting the wrapped monolith into the housing.
Typically, the paste or sheet mounting materials include inorganic binders, inorganic fibers, intumescent materials, organic binders, fillers and other adjuvants. The materials may be used as sheets, mats, or pastes. Known mat materials, pastes, and intumescent sheet materials used for mounting a monolith in a housing are described in, for example, U.S. Pat. No. 3,916,057 (Hatch et al.), U.S. Pat. No. 4,305,992 (Langer et al.), U.S. Pat. No. 4,385,135 (Langer et al.), U.S. Pat. No. 5,254,410 (Langer et al.), U.S. Pat. No. 5,242,871 (Hashimoto et al.), U.S. Pat. No. 3,001,571 (Hatch), U.S. Pat. No. 5,385,873 (MacNeil), U.S. Pat. No. 5,207,989 (MacNeil), and GB U.S. Pat. No. 1,522,646 (Wood).
The invention provides a multilayer intumescent mat or sheet that is useful as a mounting for a catalytic converter element or a diesel particulate filter or as a firestop. In one aspect, the multilayer intumescent sheet of the invention comprises at least one non-moldable flexible non-intumescent layer and at least one non-moldable flexible intumescent layer comprising an intumescent material wherein the layers form a single sheet without the use of auxiliary bonding means. In another aspect, the multilayer intumescent sheet of the invention provides at least (a) a first non-moldable intumescent layer comprising a first intumescent material and (b) a second non-moldable intumescent layer comprising a second intumescent material, the first and second intumescent materials being different, wherein the layer s form a single sheet without the use of auxiliary bonding means.
In another aspect, the invention provides a catalytic converter or a diesel particulate filter or pollution control device using a multilayer sheet of the invention. A pollution control device of the invention comprises a housing, a monolithic structure or element(s), and a multilayer intumescent sheet comprising (a) at least one non-moldable flexible non-intumescent layer; and (b) at least one non-moldable flexible intumescent layer comprising an intumescent material, said layers forming a single sheet without the use of auxiliary bonding means, said multilayer sheet being disposed between the structure and the housing to hold the structure in place.
In yet another aspect, the invention provides a pollution control device of the invention comprising a housing, a monolithic structure or element(s), and a multilayer intumescent sheet comprising at least (a) a first non-moldable flexible intumescent layer comprising a first intumescent material; and (b) a second non-moldable flexible intumescent layer comprising a second intumescent material, the first and second intumescent materials being different, said layers forming a single sheet without the use of auxiliary bonding means, said multilayer sheet being disposed between the structure and the housing to hold the structure in place.
In another aspect, the invention provides a flexible multilayer intumescent sheet useful as a firestop comprising at least (a) a non-moldable flexible non-intumescent layer comprising endothermic filler; and (b) a non-moldable flexible intumescent layer comprising an intumescent material, said layers forming a single sheet without the use of auxiliary bonding means.
In another aspect, the invention provides a process for making a multilayer intumescent sheet comprising the steps of (a) providing a first slurry and a second slurry, said first and second slurries comprising inorganic materials and at least one of the slurries contains an intumescent material; (b) depositing the first slurry onto a permeable substrate; (c) partially dewatering said first slurry to form a first layer; (d) depositing the second slurry onto said first layer; and (e) dewatering said second slurry to form a second layer, said layers forming a single sheet without auxiliary bonding means, wherein said process is a continuous process.
Known bonded multilayer mounting mats are typically made by first separately forming the layers and then bonding the layers together using an adhesive or a film or other means for example, stitches or staples. Typically, adhesively or film bonded multilayer mounting mats contain higher levels of organic material which produces undesirable smoke and odor when used in a catalytic converter. To prevent such smoke and odor, the mounting mats would have to be preheated before installation to bum off the organic bonding materials. Additionally, such mounting mats are more expensive to manufacture due to the cost of bonding the layers together and the cost of the adhesive or film used. Some disadvantages of mechanically bonded or attached multilayered mounting mats include the expense of added steps and materials and the mat may be weakened at the point of mechanical attachment such as where stitches or staples perforate the mat. Other multilayer mounting mats are comprised of separate layers that must be individually mounted within the catalytic converter housing.
A disadvantage of a single layer mat or sheet containing expandable graphite or a mixture of expandable graphite and unexpanded vermiculite is that typically, such single sheet constructions having a homogeneous or uniform composition throughout the sheet require relatively high amounts of expandable graphite for the desired low temperature expansion which increases the cost of the mat.
Some of the advantages of the present invention include, for example, that the flexible multilayer sheet: is made without adhesives or other auxiliary bonding means; can be formulated so to expand or intumesce over specific temperature ranges using relatively less intumescent material; can be made using a continuous process; is easier to handle and requires less labor to install than mats made from two or more individually bonded sheets; and requires less organic materials than adhesively bonded or laminated sheets because an adhesive is not required.